1. Field of the Invention
This invention relates generally to a flexible magnetic disc apparatus adapted to be used in an electronic still camera for recording on a flexible magnetic disc a information signals representing a still picture or image.
2. Description of the Prior Art
It has been earlier proposed to provide a flexible magnetic disc apparatus in which a flexible magnetic disc is adapted for the magnetic recording thereon of information signals, for example, representing still images, and which is contained in a protective jacket for convenience in handling and storage. In such apparatus, it is necessary that, when the flexible magnetic disc is loaded into a magnetic recording and/or reproducing apparatus included in an electronic still camera, the center of rotation of the flexible magnetic disc in the protective jacket will be precisely coincident with the axis of the driving shaft or spindle included in the disc drive unit of the magnetic recording and/or reproducing apparatus.
With the foregoing in view, it has been proposed, for example, as disclosed specifically in Japanese Laid-Open Publication No. 195674/1982 (Japanese patent application No. 82831/1981), which has a common assignee with the present application, to provide the flexible magnetic disc with a reinforcing core member secured to the disc at the center of the latter. Such reinforcing core member is formed with an aperture for receiving the driving shaft or spindle of the disc drive unit and having positioning projections defining surfaces against which the spindle is resiliently urged for making the center of rotation of the magnetic disc coincident with the axis of the spindle.
The reinforcing core member applied to the flexible magnetic disc in the above identified Laid-Open Publication is molded of a synthetic resin material and the aperture for receiving the spindle and the positioning projections extending into the aperture are molded simultaneously with the remainder of the core member. Of course, the mold used for forming the core member has a configuration corresponding to the latter, and thus is provided with a protruberant portion corresponding to the spindle receiving aperture of the molded core member. Since the positioning projections for engagement with the spindle need to be formed within the spindle receiving aperture, the mold for forming the core member is divided into an upper mold half and a lower mold half with the parting surface therebetween extending along top edges of the spindle positioning projections. The upper and lower mold halves are provided with protuberant portions that abut when molding the core member so as to form the spindle receiving aperture. As is well known, such protuberant portions of the upper and lower mold halves need to be tapered or increased in diameter in the directions toward the respective openings of the aperture to be defined thereby in order to ensure that the protuberant portions of the mold halves can be extracted from the aperture of the core member molded thereby. Of course, the operative surfaces of the positioning projections, that is, the surfaces thereof engageable with the spindle, are similarly tapered or inclined and, as a result, the spindle receiving aperture has different effective diameters at the upper and lower edges of the positioning projections. The magnetic disc apparatus disclosed in the previously identified laid-open publication is designed with the intention that a cylindrical peripheral surface of the driving shaft or spindle will engage the positioning projections at the upper edges of the latter, that is, where the aperture has the smallest effective diameter, and where the axis of the spindle will be coincident with the center of rotation of the magnetic disc attached to the reinforcing core member.
Although the height of the driving shaft or spindle is standardized, the pertinent standards specify predetermined dimensional tolerances for the manufacture of the driving shaft or spindle and for the other components of the flexible magnetic disc apparatus. It has been found that, within such dimensional tolerances, the upper margin of the cylindrical peripheral surface of the spindle may be positioned below the top edges of the positioning projections of the core member of a flexible magnetic disc mounted on the disc drive unit. In that case, the spindle will engage the tapered operative surfaces of the positioning projections below the top edges of the latter, that is, at a level where the effective diameter of the spindle receiving aperture is larger than the diameter for achieving precise centering of the magnetic disc in respect to the axis of the spindle or driving shaft.